Modern hearing assistance devices, such as hearing aids, are electronic instruments worn in or around the ear that compensate for hearing losses by specially amplifying sound. Hearing aids typically include electronic components mounted on or attached to printed circuit boards to enhance the wearer's listening experience.
To accommodate the relatively small hearing aid form factor, hearing aid radio frequency (RF) transmission lines may be implemented on flexible circuit boards. However, the performance of RF transmission lines is limited when using flexible circuit boards, especially in areas of the flexible circuit boards that are bent to accommodate the hearing aid form factor.
In order to provide a manufacturable RF transmission line for a flexible circuit bend area that provides improved RF performance, existing solutions use microstrip or stripline configurations. These microstrip or stripline configurations may use external layers. However, these microstrip or stripline exhibit excessively narrow transmission lines. Such excessively narrow transmission lines are difficult to manufacture, as the manufacturing tolerance variations tend to exceed the requirements of the narrow transmission lines. Additionally, microstrip or stripline antennas using the external layers of the flexible circuit would have problems with delamination of the copper from the flexible circuit polyimide layer.
Some existing coplanar waveguides include methods of constructing coplanar waveguides on semi-rigid boards. These are a combination regular circuit board and flexible circuit board. Other existing coplanar waveguides include an air gap within the coplanar waveguide.
What is needed in the art is an improved system that provides a manufacturable RF transmission line for a flexible circuit bend area that provides improved RF performance.